The present invention relates to a cassette for an image information recording carrier, a mechanism for removing an image information recording carrier from the cassette, and an apparatus for reading image information, and more particularly to a cassette for storing an image information carrier such as a stimulable phosphor sheet or an X-ray film, for example, under light-shielding conditions, an image information carrier removing mechanism, and an information image apparatus in which the cassette is vertically inserted and opened at its leading end to define an opening, from which an image recording carrier falls by gravity into an image readout mechanism.
There has recently been developed and widely used especially in the medical field a radiation image recording and reproducing system for producing the radiation-transmitted image of an object using a stimulable phosphor material capable of emitting light upon exposure to stimulating rays. When a stimulable phosphor is exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, or ultraviolet rays, the phosphor stores a part of the energy of the radiation. When the phosphor exposed to the radiation is subsequently exposed to stimulating rays such as visible light, the phosphor emits light in proportion to the stored energy of the radiation.
In the radiation image recording and reproducing system employing such a stimulable phosphor, the radiation image information of an object such as a human body is stored in a sheet having a layer of stimulable phosphor, and then the stimulable phosphor sheet is scanned with stimulating rays to cause the stimulable phosphor sheet to emit light representative of the radiation image. The emitted light is then photoelectrically detected to produce an image signal that is electrically processed for generating image information which is recorded on a recording medium such as a photosensitive material or displayed as a visible image on a CRT or the like. The construction and operation of an apparatus for reading radiation image information recorded on a stimulable phosphor sheet will be described by way of example with reference to FIG. 1 of the accompanying drawings.
A laser beam L of constant intensity emitted from a laser source 2 is applied to a galvanometer mirror 6, which reflects the laser beam L toward a stimulable phosphor sheet A positioned below the galvanometer mirror 6 and which deflects the laser beam L to scan the stimulable phosphor sheet A in a transverse direction or main scanning direction indicated by the arrow a. The stimulable phosphor sheet A is held in position on an endless belt 8 under vacuum that is developed by a vacuum suction device (not shown) placed between the upper and lower runs of in the endless belt 8 and that acts on the stimulable phosphor sheet A through a multiplicity of holes defined in the endless belt 8. At the same time that the stimulable phosphor sheet A is scanned in the main scanning direction, it is fed in a direction (indicated by the arrow b) substantially normal to the main scanning direction, so that the stimulable phosphor sheet A is also scanned in a subscanning direction indicated by the arrow b. Therefore, the stimulable phosphor sheet A is two-dimensionally scanned over its entire surface by the laser beam L. As the stimulable phosphor sheet A is thus scanned by the laser beam L, it emits light in proportion to image information recorded thereon, and the emitted light enters a transparent light guide 10 through an entrance end 9 disposed adjacent to the stimulable phosphor sheet A and extending parallel to the main scanning direction. The light guide 10 is progressively shaped into a cylindrical form from a flat front end 12 near the stimulable phosphor sheet A toward a substantially cylindrical opposite rear end 14 which is coupled to a photomultiplier 18. The light which has entered the entrance end 9 is collected into the rear end 14 and then applied through a filter (not shown) to the photomultiplier 18. The photomultiplier 18 converts the emitted light into an electric signal, which is supplied to and electrically processed by an image signal readout circuit 20. The processed signal is applied to a CRT 22 which displays the signal as a visible image, or is recorded on a magnetic tape 24, or may be recorded as a hard copy directly on a photographic photosensitive material.
It has been the conventional practice to store the stimulable phosphor sheet A in a cassette, and a desired radiation image is recorded on the sheet A by application of radiation to the sheet A through the cassette. Thereafter, the sheet A stored in the cassette is placed in the radiation image information readout apparatus, and taken out of the cassette for reading the recorded image therefrom.
The conventional image readout apparatus has employed a sheet removal means including a suction cup serving as a vacuum suction device for removing the sheet from the cassette and delivering the removed sheet to the image readout unit. The image readout apparatus requires a displacement mechanism for displacing the suction cup and also a control system for controlling the displacement mechanism to displace the suction cup along a desired path. The displacement mechanism is complex, and a delivery system must be provided for introducing the sheet into the image readout unit in a direction suitable for the image readout unit to read the recorded image. Therefore, the overall image readout apparatus has inevitably been large in size. The large image readout apparatus takes up a relatively large space in a facility such as a hospital which needs effective utilization of a small space available. The sheet removal means requires frequent inspection and maintenance.
In a conventional system using an X-ray film to record a radiation image, an unexposed X-ray film is stored in a cassette under light-shielding conditions. Radiation is applied to the X-ray film stored in the cassette to record the desired radiation image on the X-ray film. Subsequently, the X-ray film stored in the cassette is loaded into an automatic image developing machine, in which the X-ray film is removed from the cassette and the image is then developed. Like the aforesaid image readout apparatus, the automatic image developing machine employs a sheet removal means including a suction cup for taking the X-ray film out of the cassette. Consequently, the mechanism associated with the sheet removal means in the automatic image developing machine is complex and highly costly, and the automatic image developing machine is rendered large in size.